This is an R34 application to support the development of a standardized behavioral treatment program for selective mutism (SM) in young children aged 4-8 years old. This treatment consists of individual behavior therapy using a collaboratively developed graded hierarchy of speaking-related situations along with concurrent and complementary school and home-based exposure programs. The specific goals of this are: 1) to develop a detailed treatment manual that includes elements to integrate school and home participation, including the use of a school psychologist as a liaison with teachers to better ensure their training and participation in treatment, 2) to develop and test procedures for training therapists in the administration of these interventions, and, 3) to conduct a pilot controlled trial of the treatment that will provide treatment effect size estimates for use in planning subsequent larger controlled trials. SM is a disorder of childhood that interferes with both academic and social functioning. Recent reports suggest the disorder is much more common than previously thought with prevalence rates approaching those of more often studied disorders. Although behavior therapy is often cited as the preferred mode of treatment for SM, there have been no published studies examining the effectiveness of behavior therapy nor are there well-designed efforts to develop a standardized treatment. Although there is some evidence that treatment with SSRI medication is effective for reducing symptoms, medication treatment is not a viable option for many families of young children. This study would provide the preliminary information necessary to support a subsequent grant application for a larger controlled trial with power to examine the efficacy of the developed treatment as compared to no treatment (waiting list) or inactive treatment (support). In addition, the proposed study could provide valuable pilot data for the development of a school-based treatment model for SM that could result in significantly greater access to treatment and great public health benefit for affected children.